Semiconductor device and method for manufacturing thereof

Abstract

An insulating layer is provided with a projecting structural body, and a channel formation region of an oxide semiconductor layer is provided in contact with the projecting structural body, whereby the channel formation region is extended in a three dimensional direction (a direction perpendicular to a substrate). Thus, it is possible to miniaturize a transistor and to extend an effective channel length of the transistor. Further, an upper end corner portion of the projecting structural body, where a top surface and a side surface of the projecting structural body intersect with each other, is curved, and the oxide semiconductor layer is formed to include a crystal having a c-axis perpendicular to the curved surface.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The invention disclosed in this specification relates to a semiconductor device and a method for manufacturing the semiconductor device utilizing a semiconductor element.[0003]2. Description of the Related Art[0004]Attention has been focused on a technique of using a semiconductor thin film formed over a substrate having an insulating surface to form a transistor. The transistor is applied to a wide range of electronic devices such as an integrated circuit (IC) or an image display device (display device). Further, a technique of using a wide band gap semiconductor such as an oxide semiconductor for a semiconductor thin film that can be used for a transistor has been attracting attention.[0005]For example, Patent Document 1 shows that an oxide semiconductor including an In—Ga—Zn—O-based oxide can be used for a channel formation region of a thin film transistor.REFERENCE[0006][Patent Document 1] Japanese Published Patent ...

AI Technical Summary

Benefits of technology

[0007]In order to achieve high-speed operation and low power consumption of a transistor, high integration, cost reduction, or the like, it is necessary to miniaturize a transistor.

[0010]In view of the above, an object of one embodiment of the disclosed invention is to provide a semiconductor device which is miniaturized and in which defects are suppressed. Further, an object of one embodiment of the disclosed invention is to provide a semiconductor device having stable electric characteristics and high reliability.

[0028]According to one embodiment of the disclosed invention, a semiconductor device which is miniaturized and in which defects are suppressed can be provided. Further, according to one embodiment of the disclosed invention, a semiconductor device having stable electric characteristics and high reliability can be provided.

[0029]Further, according to one embodiment of the disclosed invention, the size of a transistor can be sufficiently reduced. When the size of the transistor is sufficiently reduced, the area of a semiconductor device is also reduced and thus the number of semiconductor devices manufactured from one substrate is increased. Thus, manufacturing costs of the semiconductor device can be saved. Since the semiconductor device is downsized, a semiconductor device with a size similar to that of the conventional semiconductor device can have improved functions. Further, the semiconductor device can be highly integrated. Furthermore, effects of high-speed operation, low power consumption, and the like can be obtained because of a reduction in channel length.

Problems solved by technology

In the case where a transistor is miniaturized, there is a problem caused by a short channel effect.

The short channel effect is likely to occur in a transistor including an oxide semiconductor particularly because such a transistor is difficult to control threshold voltage by doping, unlike a transistor including silicon.

Further, the electric characteristics of an oxide semiconductor layer might change due to irradiation with visible light or ultraviolet light, which is a factor of change in the electric characteristics of a transistor including the oxide semiconductor layer, resulting in a reduction in reliability of a semiconductor device.

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